Compositions with a polyamide or polyester matrix and ethylenic polymers are already known for their impact strength.
Patent EP 096 264 describes a material of high impact strength, containing:
a thermoplastic nylon which has a relative viscosity of 2.5 to 5, and PA1 from 5 to 60% by weight, relative to the thermoplastic nylon, of an uncrosslinked terpolymer consisting of: PA1 (a) a thermoplastic polyester PA1 (b) 1 to 100 parts of a polymer containing at least one epoxy group per molecule and having a flexural elasticity modulus of not more than 10.sup.4 kg/cm.sup.2 at ambient temperature, and PA1 (c) 0.5 to 100 parts of a copolymer of .alpha.-olefin and of an .alpha.,.beta.-unsaturated carboxylic acid, in which at least 5 mol % of the carboxylic groups are neutralized with an alkali metal, PA1 (A) 60 to 97 parts by weight of a polyamide resin containing at least 2 parts by weight of a polyamide resin which has an end COOHs/end NH.sub.2 s ratio of at least 1.5, PA1 (B) 3 to 40 parts by weight of an ethylene terpolymer including 0.3 to 10% of maleic anhydride units,
55 to 79.5% by weight of ethylene, PA2 20 to 40% by weight of at least one primary or secondary alkyl (meth)acrylate, and of PA2 0.5 to 8% by weight of a functionally acidic monomer (for example maleic anhydride). PA2 5 to 60% of alkyl acrylate units and 40 to 90% of ethylene units, PA2 and 0.01 to 20 parts by weight per 100 parts by weight of the sum (A) and (B) of a crosslinking agent which is a polyfunctional compound containing at least two groups which are reactive towards the anhydride groups of (B).
Patent EP 218 665 describes compositions containing from 50 to 95% by weight of at least one polyamide resin and 5 to 50% by weight of at least one ethylene polymer containing from 0.9 to 16 mol % of units derived from maleic anhydride and/or at least one alkyl acrylate or methacrylate in which the alkyl group has from 1 to 6 carbon atoms.
The said ethylene polymer is present in the form of a mixture of ethylene/alkyl (meth)acrylate copolymer (A) and of ethylene/maleic anhydride/alkyl (meth)acrylate terpolymer (B), the molar ratio (A)/(B) being between 1/3 and 3.
Document EP-A-072,480 is also known, which describes an impact-resistant composition including from 50 to 90% by weight of polyamide, from 1 to 45% by weight of an ethylenic ionomer resin and from 0.5 to 40% by weight of an elastomeric ethylenic copolymer.
U.S. Pat. No. 3,373,223 describes a polymer blend consisting essentially of 25 to 90% by weight of polyolefin, 5 to 70% by weight of polyamide and 1 to 10% by weight of an ethylene/(meth)acrylic acid copolymer.
Patent EP 268287 describes an impact-resistant composition including:
the parts being parts by weight per 100 parts by weight of the compound (a).
Patent EP 382539 describes a polyamide resin composition including:
In this composition a part of the polyamide resin (A) forms the matrix, the terpolymer (B) forms a so-called first-order disperse phase and the remainder of the polyamide resin of (A) forms a so-called second-order disperse phase.
Although these compositions exhibit an improved impact strength when compared with the polyamide matrix employed by itself, this improvement remains, however, insufficient for many applications requiring an excellent impact strength, especially at low temperature.
Furthermore, because of the crosslinking, these compositions exhibit high flexural moduli, and this is unacceptable when compositions which have a high flexibility are being sought.